Measuring and testing – Volume or rate of flow – By measuring vibrations or acoustic energy
Reexamination Certificate
2002-01-10
2004-04-06
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Volume or rate of flow
By measuring vibrations or acoustic energy
Reexamination Certificate
active
06715366
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a clamp-on ultrasonic flow-meter, a flow rate-measuring structure, and a ultrasonic transmitting-receiving device.
BACKGROUND OF THE INVENTION
The clamp-on ultrasonic flowmeter is attached to a outer surface of a pipe in which a fluid flows, for measuring from outside of the pipe a volume of the fluid flowing inside of the pipe. The clamp-on ultrasonic flowmeters are generally classified into two types. One utilizes a difference of propagating rates, and another utilizes the Doppler effect.
In the mode utilizing a difference of propagating rates, a pair of ultrasonic waves are propagated under such condition that one ultrasonic wave is propagated downstream to cross the stream of fluid while another ultrasonic wave is propagated upstream to cross the stream of fluid. Then, the time required for propagating the downstream ultrasonic wave between the predetermined distance and the time required for propagating the upstream ultrasonic wave between the same distance are compared to determine the flow rate.
In the mode utilizing the Doppler effect, the flow rate is determined by measuring a rate of particle or babble flowing with the fluid, under assumption that the particle or babble moves at a rate equal to that of the moving fluid. The moving rate of the particle or babble can be determined, by detecting variation of ultrasonic frequency from that of ultrasonic wave applied to the moving particle or babble to that of ultrasonic wave reflected to the moving particle or babble.
A representative constitution of a known clamp-on ultrasonic flowmeter is illustrated in
FIG. 9
in the form of a sectional view. The clamp-on ultrasonic flowmeter of
FIG. 9
utilizes a difference of propagating rates of ultrasonic wave. The clamp-on ultrasonic flowmeter is composed of a pair of ultrasonic transmitting-receiving devices
1
a
,
1
b
. The ultrasonic transmitting-receiving device
1
a
is composed of a ultrasonic transducer
2
a
and a ultrasonic propagating element in the form of wedge
3
a
. The ultrasonic propagating element
3
a
has a bottom surface
4
a
and a slanting surface
5
a
extending from one edge of the bottom surface
4
a
at an acute angle. The ultrasonic transducer
2
a
is attached on the slanting surface
5
a
. The ultrasonic transducer
2
a
has an electrode (not shown) and a lead line (not shown) on the side facing the propagating element
3
a
and on another side. The combination of the electrode and lead line serves to apply electric voltage to the transducer
2
a
. In the same way, the ultrasonic transmitting-receiving device
1
b
is composed of a ultrasonic propagating element
3
b
having a slanting surface
5
b
on which the ultrasonic transducer
2
b
is attached.
Each of the ultrasonic transducers
2
a
,
2
b
transmits ultrasonic wave to the ultrasonic propagating element when an electric voltage is applied thereto, while it produces an electric voltage when it receives ultrasonic wave. Accordingly, the ultrasonic transmitting-receiving device
1
a
,
1
b
equipped with a ultrasonic transducer functions as a transmitter and a receiver. The ultrasonic transmitting-receiving devices
1
a
,
1
b
are provided on a pipe
6
in such manner that the ultrasonic waves transmitted by the devices
1
a
,
1
b
propagate across the fluid
7
which flows inside of the pipe in the direction indicated by arrow
8
, that is, on the route
9
(indicated by a dotted line) in the directions indicated in
FIG. 9
by arrows
9
a
,
9
b.
The flow rate of the fluid
7
flowing inside of the pipe
6
is determined by the following method. First, a voltage pulse is applied to the ultrasonic transducer
2
a
of the ultrasonic transmitting-receiving device
1
a
, so as to transmit a ultrasonic wave. The ultrasonic wave propagates in the ultrasonic propagating element
3
a
, a wall of pipe
6
, fluid
7
, a wall of pipe
6
on the opposite side, and ultrasonic propagating element
3
b
on the route indicated in
FIG. 9
by the dotted line
9
. Subsequently, the ultrasonic wave is received by the ultrasonic transducer
2
b
of the ultrasonic transmitting-receiving device
1
b
, to output a voltage signal. A period of time (T
1
) from the time when the ultrasonic wave is transmitted by the ultrasonic transmitting-receiving device
1
a
to the time when the ultrasonic wave is received by the ultrasonic transmitting-receiving device
1
b
is detected. Subsequently, a voltage pulse is applied to the ultrasonic transducer
2
b
of the ultrasonic transmitting-receiving device
1
b
, so as to transmit a ultrasonic wave. The ultrasonic wave is then propagate on the same route, but in the opposite direction, and the ultrasonic transducer
2
a
of the ultrasonic transmitting-receiving device
1
a
receives the propagated ultrasonic wave. A period of time (T
2
) from the time when the ultrasonic wave is transmitted by the ultrasonic transmitting-receiving device
1
b
to the time when the ultrasonic wave is received by the ultrasonic transmitting-receiving device
1
a
is detected.
The period of time (T
1
) required for the propagation of ultrasonic wave from the device
1
a
to the device
1
b
along the arrow
9
a
differs from the period of time (T
2
) required for the propagation of ultrasonic wave from the device
1
b
to the device
1
a
along the arrow
9
b
. The period of time (T
1
) is shorter than a period of time required for propagating ultrasonic wave in still water because the ultrasonic wave from the device
1
a
to the device
1
b
is propagated at an increased rate by the aid of the flowing fluid, while the period of time (T
2
) is longer than a period of time required for propagating ultrasonic wave in still water because the ultrasonic wave is propagated from the device
1
b
to the device
1
a
against the stream of the fluid. Thus, the difference of the propagation period (T
2
-T
1
) is relative to the rate of movement of the flowing fluid
7
. Therefore, the rate of movement of the flowing fluid is calculated from the difference of propagation period. The flow rate of the fluid
7
is then determined from the difference of propagation period and the sectional area of the inside of the pipe
6
.
Thus, the clamp-on ultrasonic flowmeter is advantageous in that it can determine the flow rate with no direct contact with the flowing fluid. In order to employ the clamp-on ultrasonic flowmeter more advantageously, however, a study should be made on the clamp-on ultrasonic flowmeter for increasing the measuring sensitivity.
One main point for increasing the measuring sensitivity of the clamp-on ultrasonic flowmeter resides in prolongation of the ultrasonic wave-propagating passage in the fluid passing within the pipe (or tube). If the ultrasonic wave-propagating passage in the passing fluid is prolonged, the flow rate can be detected using the long propagating passage, and therefore the sensitivity of the flowmeter increases.
The ultrasonic wave transmitted by a ultrasonic transducer propagates to the fluid through the ultrasonic propagating element and the pipe wall. The ultrasonic wave is refracted first on the interface between the ultrasonic propagating element and the pipe wall based on the ratio of sonic propagating rate between both materials, according to the Snell's Law, and second on the interface between the pipe wall and the fluid in the same way.
Since the sonic propagating rate of the pipe wall and that of the passing fluid are predetermined, it is effective for the prolongation of ultrasonic wave passage in the passing fluid to adjust the sonic propagating rate of the ultrasonic propagating element in the wedge form to be essentially equivalent to that of the pipe wall and further to impinge the ultrasonic wave onto the pipe wall at a large angle of incidence.
Accordingly, it appears natural to make the ultrasonic propagating element using the same material as that of the pipe wall. For instance, if the pipe wall is made of fluororesin, it is assumed that the ultrasonic propagating element is favorably made of fluor
Costellia Jeffery L.
Lefkowitz Edward
Nixon & Peabody LLP
Thompson Jewel V.
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